Effects of Repeated Freezing and Thawing of Livestock and Poultry on Cholesterol and Its Oxide Contents

Effects of repeated freezing and thawing on the quality of livestock and poultry meat from the changes of cholesterol and cholesterol oxides,water and malondialdehyde in livestock and poultry meat were studied. The cholesterol and 5 cholesterol oxides(25-hydroxycholesterol,7β-hydroxycholesterol,20α-hydroxy-cholesterol,5α,6α-epoxy-based cholesterol,7-keto cholesterolcontent)in meat after repeated freezing and thawing 7 times(fresh meat recorded as freezing and thawing 0 times)were determined by gas chromatography-tandem mass spectrometry/mass spectrometry(GC-MS/MS). The results showed that,as the number of freeze-thaw cycles increased,the cholesterol content gradually decreased. Among them,the cholesterol content in beef especially reduced(the reduction was 32.47 μg/g).In the process of repeated freezing and thawing,the content of cholesterol oxide increased gradually and then stabilized. Among them,the increase of 7β-hydroxycholesterol content in chicken thighs was the most significant(increase amount was 0.601 μg/g).In addition,the moisture content and malondialdehyde content in the process of lipid peroxidation in livestock and poultry meat were investigated. The moisture in the chicken breast reduced most(the reduction was 14.472 g/100 g)and the largest increase in malondialdehyde was in beef(in increments of 1.004 μg/g). Repeated freezing and thawing would lead to increased cholesterol oxidation and lower quality of livestock and poultry.